Tom, Here are the best pics I have. I'm at work in Pennsylvania at the moment, but can take more pics when I get home.
The mains are offset, and there are only three- this is on of my biggest concerns. The other big concern is 'splitting the block. Other than the front and rear of the block, there is only the one center web you see in the pic. It is also the only water passage from one side of the block to the other, and is one of the areas prone to cracking. This is the main reason for the 1/2" top plate across the engine.
You're right about the bottom end- it's heck for stout! Add a crank girdle, bigger mains, and the top plate, and I think it will be a beast!
Rex, yes, it is a very iconic engine, at least as far as Caddy flatheads go. You know these engines are the same ones that were used in tanks in WWII, correct?
As for 5000 rpm, the engines were rated as 3450 rpm's in passenger cars, although the military did a lot of testing at 4000rpm. 150hp, and 260 lbs torque- monsters in there day! The camshaft is a reground, factory, one piece cast iron, 1.375" in diameter! The gear on the back of it was part of the one piece cast. Sorry, I don't have any pics of the head chambers, but I'll see if Aaron will send me some.
And yes, we have incorporated many of the feature- blower, big valves, pop-up pistons, dual water feeds, extra head bolts, etc.
...and a whole lot of trick stuff they didn't!